This invention relates to a tire and/or wheel assembly for a vehicle, aimed at improving the propelling of a surface vehicle.
It is generally known that in order to provide effective maneuverability of a surface vehicle, its rim-mounted tires should be inflated to their inflation pressure, while puncture of a tire envelope especially in the sidewall of such tire may cause a very rapid loss of internal inflation pressure. Known techniques aimed at solving a problem of driving the vehicle upon deflation of its tire are associated with the provision of sensors or deflation warning devices capable of earlier detection of a change in the gas pressure within the tire in order to warn the user of a loss of pressure, as well as provision of various facilities for delaying effects of puncture on tires for as long as possible. For example, a tire of the conventional type may be provided thereinside with various elements, some including elastomers such as rubber polyurethanes and others, such that, in the event of puncture of the main outer tire or loss of pressure by the latter, the inner structure might serve as a support for the outer tire. Devices are also known which are placed inside the tire and which, though not inflated in normal use, may reduce pressure loss in the tire in the event of puncture of the latter. Moreover in a standard tire there is a strong dependency between the pressure and the tire ability to withstand torque and lateral forces, i.e. the less internal pressure in a standard tire the less stable it will be and its accurate steering ability will be reduced.
General Description
The present invention provides a novel locomotion assembly which can be used for carrying and propelling a surface vehicle. More specifically, the present invention provides a novel approach for the configuration of a surface vehicle's tire. The tire of the invention may be configured as gas envelope, while in some embodiments the gas can be air. The configuration of the tire of the present invention is such that the technological procedure associated with the tire inflation may be eliminated or at least significantly reduced.
In this connection, the following should be understood. As indicated above, in order to provide effective maneuverability of a surface vehicle, its wheel assembly should be substantially flexible in order to deform, and while deforming the wheel assembly would better follow the contact surface allowing for better traction and at the same time the flexibility will allow for shock absorption that contributes both to ride comfort and general stability and safety of the vehicle. In many cases the flexibility is gained by using gas (mostly air) inflating the tire. A standard tire consists of a closed inflated flexible envelope, where the gas/air stretches the envelope substantially to its full radial dimension therefore defining substantially the largest potential volume for the given envelope, any flexibility or deformation in such tire envelope involves deflection and stretching in the surface of the envelope. The deformation generates heat and causes fatigue resulting in wear-out and energy loss. Moreover, the way that said deformation accrued, will not allow sufficient contact between the deflected area of the tire (the contact patch of the tire tread) and the surface, as will be described further below.
The present invention provides a semi-flexible envelope that by mathematical definition defines a volume that is substantially smaller than the theoretical volume which such envelope can potentially define, i.e. when compressed with gas the envelope is limited by its unique structure thus preventing stretching towards its maximum volume. Moreover, the profile of the envelope allows deformation of the tire when loaded or when depressurized in a way that the tread part of the tire maintains a good constant contact with the surface, as well as maintains its ability to deliver torque and bear side forces from the vehicle to the ground, and generates substantially less heat while doing so.
The sidewall of the tire of the present invention presents a combination of curved surfaces. To this end, a combination of curved surfaces can be described as a combined surface formed by an infinite number of points that maintain a relation between them, i.e. relative distance to one another along the surface, such that curving or folding of the surface will not change the relation between the points along the surface, and therefore will not involve stretching or deflection in the surface. In contrary, the sidewall of a standard tire can be defined as a spherical surface which can be described as an infinite number of points that maintain singular relation, i.e. any change in the sphere will result in a change in relation between some of the points, and will thus involve stretching and deflection, that in many cases generate heat and may cause fatigue in the surface material.
Thus, by one broad aspect of the invention there is provided a wheel assembly for a surface vehicle, comprising a tire envelope configured to be mountable on a wheel hub, the tire envelope by its inner surface defining a gas cavity having a certain maximal volume defined by a geometry of the envelope (namely the maximal volume achievable in the absence of structural constraints), wherein the tire envelope comprises or defines a suspension assembly within its side walls (e.g. a suspension assembly embedded in side walls of the tire envelope). Consequently under gas pressure in said cavity the volume achievable through gas-pressure imposed expansion is substantially smaller than said maximal volume defined by the geometry of the envelope.
The tire of the present invention can be filled by gas/air to better suspend a vehicle, but has no such requirement for delivering torque or to withstand side forces. The tire can be designed to operate as pneumatic tire while using the gas/air as a suspension shock absorbent, however it may function safely with no gas/air, being designed as a non-pneumatic wheel and exploiting its structure to deliver torque and bear side forces. The non-pneumatic configuration is useful also in cases when gas/air cannot be used or its use is undesirable, such as in a Luna vehicle for example.
The tire has an outer, surface-engaging side (termed “tread”, having a circumferential surface), and opposite side surfaces/walls which are integral with and extend from the surface-engaging side and by their free ends define an inner, rim-engagement side, of the tire by which the tire is connectable to the locomotion assembly. According to the invention, each of the opposite side walls of the tire has a pattern in the form of a surface relief, which in some embodiments defines at least one groove which has a substantially V-shaped cross-section and is located between the surface-engaging side (tread) and the rim-engagement side. Such a groove with substantially V-shaped cross section is referred to below as a V-shaped groove. It can also be described as if each V shape groove divides the sidewall into 2 two-dimensional curved surfaces.
Thus, by such embodiments the side wall has a surface pattern defining one or more V-shaped grooves extending between the surface engaging side and the ring-engagement side (i.e. along the radial axis of the tire). The provision of such grooves which are made in a generally flexible/elastic tire material and which have substantially round apexes provides the tire with a desired suspension assembly. This allows the tire (locomotion assembly) containing very low air pressure (even zero pressure inside) to be still able to withstand forces and rotate and drive the vehicle with sufficient maneuverability.
Generally, the required V-shape geometry of the groove may be achieved by any suitable apex angle. In some embodiments, the intersecting sides of the V-shape groove are formed by a pair of opposite segments of substantially frustum-conical structures (or generally conoid structures). The general concept of using frustum-conical structure in locomotion assembly of a surface vehicle is described in the International (PCT) application No. PCT/IL2011/000115, which is assigned to the assignee of the present application. According to this technique, the locomotion assembly has a frustum-conical structure including at least one pair of flexible members each having a frustum-conical surface extending between its relatively narrow and wide ends along a frustum-conical axis. The frustum-conical members of the pair are arranged in a substantially symmetric manner and are rotatable about a common axis coinciding with their frustum-conical axes. Each frustum-conical member is reversibly deformable from its biased rounded shape corresponding to a frustum-conical shape in which its side elevation is circular into a deformed frustum-conical shape in which its side elevation is non-circular. The frustum-conical members of the pair are configured and operable such that a bias of each of the frustum-conical members to induce the surface engaging member to move in a non-linear direction is offset by the other frustum-conical member of the pair'.
According to the present invention, the tire constitutes a wheel-tire unit which may be constituted just by the above described envelope structure of elastomeric material composition (or semi elastomeric materials) enclosing a cavity/lumen which may or may not be filled by gas medium. The tire is preferably configured to have desired rigidity and flexibility distribution along and across its sides. To this end, rigidity and flexibility may be different at different regions of the side wall, i.e. the side walls might have a certain rigidity/flexibility pattern at least along the radial axis (radial pattern) of the tire and in some embodiments a further rigidity/flexibility pattern along the circumference of the side wall (circumferential pattern). These different levels of rigidity and flexibility can be achieved by several ways, which may include implantable/embedded rigid material such as plastics, steel, spring etc., the rigidity may be gained by forming a ‘beam’ structure using combination of non streaking elements such as cables, or cords such as textile cords nylon, Kevlar, etc. and/or relatively hard/stiff elastomers such as hard rubber, as will be described more specifically further below.
In case the envelope is filled with compressed gas/air, the structure has to eliminate the gas from bulging the envelope to define the biggest possible volume it can. Therefore a certain restrain has to be set in order to keep the desired shape of the envelope. The inner part of the groove (closer to the rim/hub engagement side of the tire) tends to increase its diameter. Therefore, constructing the inner side of the groove with un-stretchable elements will support the envelope structure, preventing the inner side from ‘bulging’ out.
Moreover, in order for the inner and outer sides of the groove to withstand the gas/air pressure, both the inner and outer sides of the groove are sufficiently rigid along the radial axis of the tire. In some embodiments of the invention, it is desirable to maintain the radial rigidity of the groove sides but at the same time to gain circumferential flexibility, therefore the groove structure might be strengthened in an uneven way so it may contain relatively rigid elements only along the radial axis, or it may be designed in a way that an array of pattern elements (slots, projections, thinner regions) is provided which are arranged in a spaced-apart relationship circumferentially around the groove side(s) thereby weakening the circumferential structure while keeping the radial rigidity. A similar principle may be applied where an array of bulges extend circumferentially around the groove side(s) providing similar results.
Thus, the tire may have a certain rigidity pattern across its side walls, i.e. between the surface-engaging and rim-engagement sides. This pattern is defined by that the apex of the groove and its corners at opposite sides of the groove are sufficiently elastic (e.g. achieved by making the tire with smaller thickness within these regions) as compared to the tire regions between them. As a result, the two parts of the groove function as two beams that can be bended but not deformed. The general shape of such grooved tire is maintained and any change is reversible. On the other hand, the tire should have sufficient flexibility to absorb the forces falling on it while not breaking down. Additionally, the inner side of the groove might have a relatively higher rigidity, with respect to both “radial” and “circumferential” rigidities, in order to maintain the generally wheel-like shape of the tire, and the outer part of the groove (closer to the surface-engaging side of the tire) might be of relatively lower rigidities.
Thus, the desired combination of rigidity and flexibility can be achieved by the provision of appropriate rigidity pattern in the generally flexible material of the tire, i.e. higher radial and circumferential rigidity at the inner part of the groove than that of the outer part, while securing three flexing points along the radial direction, i.e. at the apex and corners at opposite sides of the V-shaped groove. As indicated above, a second rigidity pattern can be provided as a circumferential pattern along the circumferential direction of the inner and outer parts of the groove. This may be achieved by an array of spaced-apart slots (e.g. regions with implanted material of different rigidity than in spaces between the slots and/or uneven wall thickness) arranged along the groove with the slots' orientation being substantially perpendicular to the tire plane (across the groove). Thus, the tire with such groove extending along its circumference has a first rigidity pattern in a radial direction of the tire (across the groove) and possibly also a second rigidity pattern in a circumferential direction.
Thus, according to another broad aspect of the invention, there is provided a tire envelope for a surface vehicle, comprising a surface pattern in its side walls extending between a surface-engaging side and a rim-engagement side of the tire, said surface pattern configured as a suspension assembly embedded in the side walls to thereby prevent stretching of the tire envelope towards its maximal volume when the envelope is compressed with gas, while allowing deformation of the tire envelope when loaded or depressurized such that the surface engaging side of the tire maintains a substantially constant contact with the surface.
According to yet another broad aspect of the invention, there is provided a tire for a surface vehicle, the tire comprising an envelope structure which by its inner surface encloses a cavity, said envelope structure comprising an outer, surface-engaging side having a circumferential surface, opposite side walls which are integral with and extend from said surface engaging side, the sides walls by their free ends defining an inner, rim-engagement side of the tire by which the tire is connectable to a locomotion assembly, wherein each of the opposite side walls comprises a surface pattern extending between the surface-engaging side and the rim-engagement side and defining a surface relief in the form of at least one groove having substantially V-shaped cross section, and wherein each of the side walls is configured with a predetermined rigidity pattern across the side wall.
The rigidity pattern may comprise relatively small rigidity and thus relatively high flexibility of regions of the tire at apex of the V-shaped groove and corners defined by connection between the groove with respectively the surface engaging side and the rim engagement side of the tire.
The rigidity pattern may comprises different rigidities of the tire within respectively an outer side of the groove closer to the surface engaging side and an inner side of the groove closer to the rim engagement side of the tire. For example, the inner side of the groove comprises an array of support elements embedded therein and extending along at least one of radial and circumferential axes of the tire.
The surface engaging side is configured to have predetermined rigidity along a circumferential axis of the tire. To this end, the surface engaging side may comprise an array of support elements embedded therein.
Alternatively or additionally, the rigidity pattern may be formed by varying thickness of at least one of the outer and inner sides of the groove.
Generally speaking the grooved side walls of the tire and appropriate rigidity/flexibility distribution of the tire material within the tire creates an optimal suspension assembly allowing the effective operation of a locomotion assembly using such tire with practically no limitations to the lack/reduction of pressure in the tire cavity.
As indicated above, the tire regions at the apexes of the grooves (and outer corners) are relatively flexible. It has been realized in accordance with an embodiment of this invention that in a deformable wheel the flexible portions of the side walls (particularly at said apexes), considerable strains may develop. The present invention offers a solution to reduce such strains by providing a specifically designed load-bearing arrangement.
The present invention thus in its yet further aspect provides a deformable wheel assembly with an inflatable enclosure defined by the above described tire, and a load-bearing arrangement formed by a plurality of support elements, comprising a first array of spaced-apart elements and a second array of spaced-apart elements, the elements in each of the arrays defining together a substantially frustum-conical structure (i.e. the lines that link defined points at distal ends of the elements together define a frustum-cone), the two frustum-conical structures intersecting one another with the elements of one dove-tailing those of the other structure.